A 0.65 Ma chronology and incision rate assessment of the NW Iberian Miño River terraces based on 10Be and luminescence dating

Abstract

In this work a series of 5 luminescence and 10Be dated fluvial terraces of the Miño River (NW Iberian Atlantic Margin) is presented. The outcomes allowed answering the longstanding question whether the Miño valley infill has a fluvial or marine origin. The perfect exponential decrease in 10Be concentrations with depth and a progressive increase in age with terrace altitude indicate that the Miño terraces are fluvial terraces rather than terraces incised in older marine basin infill. Accurate dating of the terraces was difficult due to saturation of the luminescence signal and high inheritance of 10Be concentrations. Nevertheless, minimum ages of up to 650ka could be determined and are very likely close to the real ages of the terraces.The age estimations and field evidence suggest that terrace formation and terrace incision occurred during eccentricity-forced cycles of glacio-eustatic sea level changes and tectonic uplift. The occurrence of a steep and narrow continental shelf probably favoured rapid and profound incision by the Miño River during periods of low sea levels. It is furthermore hypothesised that the transition periods between glacials and interglacials were especially important for terrace deposition and incision. Denudation rates of the terraces were calculated from the 10Be data and do not exceed 1.30mMa−1. These extremely low rates are probably the result of a combination of factors that favoured terrace preservation. Large, flat terrace surfaces with high permeability and continuous vegetation cover during the Quaternary stabilised the terrace surfaces.Maximum incision rates, calculated from terrace age and altitude, are 0.07–0.09mka−1. These values can be used as proxies for tectonic uplift rates. They are in agreement with published uplift rates along the northern Spanish coast and the westernmost termination of the Cordillera Cantabrica. This similarity most likely identifies a common tectonic regime leading to similar tectonic uplift rates. The results demonstrate that tectonic uplift occurs in a region that was until very recently considered as tectonically stable.